AGEING OF CENTRIFUGAL COMPRESSORS

Centrifugal compressors operating in hydrocarbon service are increasingly required to function beyond their nominal design life. While thermodynamic performance degradation can be quantified through conventional analysis, integrity degradation associated with corrosion, fatigue, and geometric modification of pressure- retaining components requires more structured evaluation. This paper investigates ageing-related integrity risks in centrifugal compressor casings, with emphasis on corrosion-induced material loss and its influence on stress redistribution in critical regions such as shear-ring grooves. A combined inspection-based and analytical approach is presented. Field observations from ageing offshore compressors are integrated with established degradation mechanisms, including corrosion, erosion, fatigue, and sulphide stress cracking. Finite Element Analysis (FEA) is employed to evaluate stress amplification resulting from corrosion depths within typical corrosion allowance limits. Results indicate that moderate geometric loss (<3 mm) may increase peak local stresses by approximately 20%, with implications for fatigue margin and structural reliability. A structured lifecycle integrity framework is proposed, incorporating risk-based inspection, degradation assessment, maintenance strategy review, and verification of material properties in accordance with fitness-for-service principles. The findings support a transition from experience-based ageing management toward analytically supported integrity verification for extended operation of centrifugal compressors.